Solidifying material for cell electrode solution, and cell comprising the solidifying material

ABSTRACT

A solidifying material for a cell electrolyte solution is a block copolymer, which comprises, as segments A, a polymer non-compatible with the cell electrolyte solution and, as segments B, a polymer compatible with the cell electrolyte solution. The solidifying material absorbs and solidifies the cell electrolyte solution. A smallest unit of the block copolymer is A-B-A. To each of the segments B, at least one group selected from the group consisting of a carboxyl group, an ester group, a hydroxyl group, a sulfonic group, an amino group, a cyclic carbonate group and a polyoxyalkylene group is bonded via a —S— bond or a —C— bond.

BACKGROUND OF THE INVENTION

[0001] a) Field of the Invention

[0002] This invention relates to a solidifying material for cell orbattery (hereinafter collectively called “cell”) electrolyte solutionand a cell comprising the solidifying material as a constituent element.The term “cell electrolyte solution” may hereinafter be referred tosimply as an “electrolyte solution”, and the term “solidifying materialfor an electrolyte solution” may hereinafter be referred to simply as“solidifying material”.

[0003] b) Description of the Related Art

[0004] As a cell electrolyte is conventionally in a liquid form, it issealed in a case from the standpoint of safety. To safely hold theelectrolyte solution over a long time, the case is required to bestrongly built. As a result, it has heretofore been difficult to form acell into a thin structure. It has recently been proposed to have anelectrolyte solution absorbed in a high molecular substance such thatthe electrolyte is solidified. This approach is expected not only toavoid leakage of the electrolyte solution from cells and to provide thecells with improved safety but also to achieve higher design toleranceson cell configurations, cell thickness reductions, improvements indurability, and higher outputs owing to increases in area.

SUMMARY OF THE INVENTION

[0005] The conventional high molecular substances for solidifyingelectrolyte solutions have crosslinked structures, are insoluble insolvents, and do not melt under heat. Accordingly, they cannot be formedinto thin films of uniform thickness. Use of a solid electrolyte in theform of a thin film is indispensable for the construction of a cell ofsmaller dimensions, especially of a reduced thickness. Because theabove-described high molecular substances cannot be formed into thinfilms, it has heretofore been difficult to obtain a solid electrolyte inthe form of a thin film of uniform thickness.

[0006] An object of the present invention is, therefore, to provide asolidifying material for a cell electrolyte solution, which can beformed into a thin film or sheet (which may hereinafter be collectivelycalled “film”) of uniform thickness and can easily absorb and solidifythe electrolyte solution.

[0007] Another object of the present invention is to provide a cellmaking use of such a solidifying material.

[0008] The above-described objects can be achieved by the presentinvention as will be described hereinafter.

[0009] Described specifically, the present invention, in a first aspectthereof, provides a solidifying material for a cell electrolytesolution, characterized in that the solidifying material is a blockcopolymer comprising, as segments A, a polymer non-compatible with thecell electrolyte solution and, as segments B, a polymer compatible withthe cell electrolyte solution, and absorbs and solidifies the cellelectrolyte solution, a smallest unit of the block copolymer is A-B-A,and to each of the segments B, at least one group selected from thegroup consisting of a carboxyl group, an ester group, a hydroxyl group,a sulfonic group, an amino group, a cyclic carbonate group and apolyoxyalkylene group is bonded via a —S— bond or a —C— bond; and a cellcomprising the solidifying material as a constituent element.

[0010] The present invention, in a second aspect thereof, also providesa solidifying material for a cell electrolyte solution, characterized inthat the solidifying material is a graft copolymer comprising, assegments A, a polymer non-compatible with the cell electrolyte solutionand, as segments B, a polymer compatible with the cell electrolytesolution, and absorbs and solidifies the cell electrolyte solution, andto each of the segments B, at least one group selected from the groupconsisting of a carboxyl group, an ester group, a hydroxyl group, asulfonic group, an amino group, a cyclic carbonate group and apolyoxyalkylene group is bonded; and a cell comprising the solidifyingmaterial as a constituent element.

[0011] The present invention, in a third aspect thereof, also provides asolidifying material for a cell electrolyte solution, characterized inthat the solidifying material comprises a film or sheet of a polymerhaving properties that the polymer is insoluble in the cell electrolytesolution but the polymer absorbs and solidifies the cell electrolytesolution, and a backing reinforcing the film or sheet, and the backingis a woven fabric, a nonwoven fabric or a porous film; and a cellcomprising the solidifying material as a constituent element.

[0012] The solidifying materials according to the present invention canbe dissolved or finely dispersed in appropriate solvents or can becaused to melt by heat, so that they can be formed into films each ofwhich has a desired thickness. Namely, the solidifying materialsaccording to the present invention can be formed into thin films ofuniform thickness, and can easily absorb and solidify cell electrolytesolutions. As these films can be provided with enhanced strength byreinforcing them with backings, these films can each be formed with astill reduced thickness. These film-shaped solidifying materials canconveniently absorb and solidify electrolyte solutions, and thethus-solidified electrolyte solutions have good electrical conductivityand are useful as solid electrolytes for cells. Upon absorption ofelectrolyte solution in each of these films, the volume of the filmincreases in the direction of its cross-section, in other words, towardan associated electrode, so that the contact between the electrode andthe film is rendered closer an surer. Especially when a woven fabric isused as a backing, a reduction in electrical conductivity can beminimized because the woven fabric has adequate strength despite itslarge opening area and moreover, a solidifying material having a largeparticle size can also be used for the preparation of a coatingformulation which is useful for forming a film.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0013] (First Aspect of the Present Invention)

[0014] The solidifying material according to the first aspect of thepresent invention is characterized in that the solidifying material is ablock copolymer comprising, as segments A, a polymer non-compatible withthe cell electrolyte solution and, as segments B, a polymer compatiblewith the cell electrolyte solution, and absorbs and solidifies the cellelectrolyte solution; a smallest unit of the block copolymer is A-B-A;and to each of the segments B, at least one group selected from thegroup consisting of a carboxyl group, an ester group, a hydroxyl group,a sulfonic group, an amino group, a cyclic carbonate group and apolyoxyalkylene group is bonded via a —S— bond or a —C— bond.

[0015] The block copolymer employed as a raw material for thesolidifying material is a block copolymer of segments A and segments B.Each segment B contains an unsaturated double bond group. Such feedblock copolymers are disclosed, for example, in Kogyo Zairyo (IndustrialMaterials), “Tokushu—Netsukasosei Elastomers (SpecialEdition—Thermoplastic Elastomers”, 24(12) 1976 and Sekiyu Gakkai Shi(Bulletin of the Japan Petroleum Institute), 18, 565 (1975). These blockcopolymers are high molecular substances each of which has a structuresuch as (Segment A)-(Segment B)-(Segment A) that the segment B, whichhas an unsaturated double bond, is flanked at two points thereof betweenthe segments A, as expressed under the name of the so-called tele-blockcopolymer type, multi-block copolymer type or star-shaped blockcopolymer type. Further, a single-block copolymer composed of segments Aand segments B may also be mixed in these high molecular substances.Preferably, each of these high molecular substances has a weight averagemolecular weight of from 10,000 to 500,000.

[0016] As the segments A which constitute the solidifying materialaccording to the first aspect of the present invention, a polymerselected from polystyrene, polyethylene or polypropylene is preferred.As the segments B, on the other hand, a polymer selected frompolybutadiene, polychloroprene or polyisoprene is preferred. Thesegments A are in a crystallized form in the block copolymer, and keepthe block copolymer physically crosslinked at room temperature. Further,these segments A have high non-compatibility (insolubility) with a cellelectrolyte solution, for example, a thick aqueous solution of potassiumhydroxide.

[0017] The content of the segments A in the block copolymer canpreferably be in a range of from 0.5 to 70 wt. %. A content lower than0.5 wt. % is too low to exhibit the crystallization effect of thesegments A for the copolymer. A content higher than 70 wt. %, on theother hand, results in a solidifying material having a smaller liquidabsorption rate for the electrolyte solution. The preferred content isin a range of from 1.0 to 50 wt. %.

[0018] The segments B which also constitute the solidifying materialaccording to the first aspect of the present invention is a polymerselected from the group consisting of polybutadiene, polychloroprene andpolyisoprene, and the polymer can preferably have a weight averagemolecular weight of from 10,000 to 300,000. The content of the segmentsB in the block copolymer may be 99.0 to 50 wt. %, preferably 95.5 to 30wt. %.

[0019] Each segment B has a group, which is compatible with theelectrolyte solution, via a —S— bond or a —C— bond. Examples of thecompatible group can include a carboxyl group, ester groups, a hydroxylgroup, a sulfonic group, an amino group, cyclic carbonate groups, andether groups. Illustrative of the ether groups are homopolymers andblock or random copolymers of polyoxyethylene groups or polyoxypropylenegroups. The ester group, through its hydrolysis or the like, can makethe segment B exhibit compatibility with the electrolyte solution. Thesecompatible groups should be suitably selected and combined dependingupon the electrolyte solution. For example, electrolyte solutionsinclude both aqueous and non-aqueous systems. It is preferred to selectsuch compatible groups as permitting absorption of a solution of one ofthese systems and to introduce them into the segments B.

[0020] As an illustrative method for the introduction of theabove-described compatible groups into the segments B, a compatiblecompound containing one mercapto group (—SH), acid sodium sulfite(sodium hydrogensulfite) or maleic anhydride is added to double bonds inthe segments B. Examples of the mercapto-containing compound can includethioglycolic acid, thiolactic acid, thiomalic acid, thiosuccinic acid,thiosalicylic acid, mercaptopropane-sulfonic acid, thioethanolamine,thioglycol, and thioglycerin. In the presence of a free radicalgenerator, for example, azobisisobutyronitrile, azobiscyanovaleric acid,benzoyl peroxide, lauroyl peroxide, cumene hydroperoxide, ammoniumpersulfate or an alkali salt thereof, or hydrogen peroxide, or by simplyheating, the mercapto compound, maleic anhydride or acid sodium sulfiteis added to the segments B to obtain the solidifying material accordingto the first aspect of the present invention.

[0021] The introduction of polyethylene oxide groups or polypropyleneoxide groups into the segments B via —C— bonds or —S— bonds can beeffected by introducing hydroxyl groups or carboxyl groups into thecopolymer in accordance with the above-described method and thenaddition-polymerizing ethylene oxide or propylene oxide to the groups sointroduced. The polyethylene oxide groups or polypropylene groups soadded may preferably have a weight average molecular weight in a rangeof from 200 to 1,000.

[0022] Upon introduction of the compatible groups, it is preferred toconduct the introduction by using a solvent. Preferred examples of thesolvent can include cyclohexane, methylcyclohexane, toluene, xylol,terpene, pentane, naphthene, kerosene, methyl ethyl ketone, acetone,tetrahydrofuran, dimethylformaldehyde, dioxolane, dioxane,ethylcellosolve, diethylcellosolve, ethyl acetate, propyl acetate, butylacetate, butyl alcohol, propyl alcohol, isopropyl alcohol, ethylalcohol, methanol, and water.

[0023] The solidifying material according to the first aspect of thepresent invention obtained as described above can take any form,including a form in which the solidifying material is dissolved in anaqueous system, including a form in which the solidifying material isdispersed in water, a form in which the solidifying material isdispersed in a solvent, a form in which the solidifying material isdissolved in a solvent, and a powdery form. The production processitself of the solidifying material obtained as described above isdisclosed in JP 1-168968 A in the name of Dainichiseika Color &Chemicals Mfg. Co., Ltd.

[0024] (Second Aspect of the Present Invention)

[0025] The solidifying material according to the second aspect of thepresent invention is characterized in that the solidifying material is agraft copolymer comprising, as segments A, a polymer non-compatible withthe cell electrolyte solution and, as segments B, a polymer compatiblewith the cell electrolyte solution, and absorbs and solidifies the cellelectrolyte solution; and to each of the segments B, at least one groupselected from the group consisting of a carboxyl group, an ester group,a hydroxyl group, a sulfonic group, an amino group, a cyclic carbonategroup and a polyoxyalkylene group is bonded.

[0026] Illustrative of the segments A are polystyrene, polyethylene,polypropylene, poly(meth)acrylate esters and polyacrylonitrile, each ofwhich has a weight average molecular weight of form 3,000 to 20,000 andcontains an α,β-ethylenically unsaturated group at an end thereof. Aweight average molecular weight lower than 3,000 is too low to make thesegments A exhibit their crystallization-dependent, physicalcrosslinking effect in the graft copolymer. A weight average molecularweight higher than 20,000, on the other hand, makes it difficult toproduct the graft copolymer. The content of the segments A maypreferably be in a range of from 1 to 70 wt. %. A content lower than 1wt. % cannot exhibit the crosslinking effect of the segments A throughcrystallization, while a content higher than 70 wt. % leads to asolidifying material having a small absorption for an electrolytesolution. Contents outside the above range are not preferredaccordingly. More preferably, the content is in a range of form 2.5 to50 wt. %.

[0027] Examples of a monomer, which has a group compatible with theelectrolyte solution and is to be graft-copolymerized with the segmentsA, can include (meth) acrylic acid, maleic acid, vinylbenzoic acid,(meta)styrenesulfonic acid, 2-acryloylamido-2-methyl-1-propanesulfonicacid, methacryloxypropylsulfonic acid, vinylsulfonic acid, alkali metalsalts such as polyoxyethylene alkyl ether sulfosuccinic acid or alkalinemetal salts thereof, 4-vinylpyridine, 2-vinylpyridine,dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate,(2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, and 2-hydroxypropyl (meth)acrylate.

[0028] From these monomers, a preferred monomer is selected dependingupon the electrolyte solution. Electrolyte solutions include bothaqueous and non-aqueous systems. It is preferred to graft-polymerizesuch a monomer as permitting absorption of a solution of one of thesesystems. Two or more of the monomers may be graft-copolymerized asneeded.

[0029] When the solidifying material according to the second aspect ofthe present invention is used for a non-aqueous electrolyte solutionrepresented by an electrolyte solution for lithium cells, a monomerusable for the production of the segments B is a monomeric ester havinga general polymerizable unsaturated group. Illustrative of such amonomeric ester are methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl(meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, lauroyl(meth)acrylate, stearyl (meth)acrylate, acrylonitrile, styrene, vinylacetate, (2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate, (meth)acryloyl-containing polyethylene glycol (weight average molecularweight: 200 to 1,000), (meth)acryloyl-containing polypropylene glycol(weight average molecular weight: 200 to 1,000), and(meth)acryloyl-containing polyethylene glycol/polypropylene glycolcopolymer (weight average molecular weight: 200 to 1,000).

[0030] Among these, monomers important for the formation of segments B,which are suited for the transfer of ions in a non-aqueous electrolyteemployed in cells, are monomers containing polyoxyalkylene groups whichinclude at least a polyethylene glycol group. Use of a monomer, whichcontains a polyethylene glycol group as is or contains a copolymer ofethylene oxide and propylene oxide, is preferred.

[0031] To enhance the insolubility of the solidifying material accordingto the second aspect of the present invention in the electrolytesolution, a polyfunctional monomer may also be copolymerized in a smallproportion upon conducting the graft copolymerization. Examples of sucha polyfunctional monomer can include aromatic divinyl compounds such asdivinylbenzene and divinylnaphthalene; and (meth)acrylates such aspolyethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,tripropylene glycol di(meth)acrylate, hydroxypivalate ester neopentylglycol di(meth)acrylate, trimethylol propane tri(meth)acrylate,pentaerythritol tri (meth) acrylate, and dipentaerythritol hexa(meth)acrylate. These polyfunctional monomers can be added preferably in aproportion of 5 wt. % or less of the above-mentioned monofunctionalmonomer.

[0032] As a polymerization initiator usable upon graft copolymerization,the same polymerization initiator as that described above in connectionwith the first aspect of the present invention can also be used.Further, as a solvent usable upon graft copolymerization, the samesolvent as that described above in connection with the first aspect ofthe present invention can also be used.

[0033] The solidifying material according to the second aspect of thepresent invention obtained as described above can take any form,including a form in which the solidifying material is dissolved in anaqueous system, including a form in which the solidifying material isdispersed in water, a form in which the solidifying material isdispersed in a solvent, a form in which the solidifying material isdissolved in a solvent, and a powdery form. The production processitself of the solidifying material obtained as described above isdisclosed in JP 2-1715 A and JP 2-265909 in the name of DainichiseikaColor & Chemicals Mfg. Co., Ltd.

[0034] The solidifying material according to each of the first andsecond aspects of the present invention may preferably be in the form ofa film. Examples of a film-forming process can include the castingprocess in which a solution or dispersion of the solidifying material iscast and dried, the extrusion process in which the solidifying materialin a powdery form is dispersed in a thermoplastic resin and theresulting dispersion is extruded, and a process in which such adispersion is formed into a film by calendering. Especially in order toimpart excellent strength to a film to be obtained, a natural orsynthetic resin insoluble in the electrolyte can be added to thesolution or powder of the solidifying material.

[0035] Illustrative of the natural or synthetic resin are naturalrubber, and synthetic rubbers such as chloroprene, isoprene, butylrubber, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer,and hydrogenation products thereof. These copolymers can each be of anyone of bonding types of random bonding, block bonding and graft bonding.The content of the natural or synthetic resin is preferably 85 wt. % orless based on the solidifying material. A content higher than 85 wt. %results in a film-shaped solidifying material, the electricalconductivity of which is too low to use it as a solidifying material. Asa still further additive, a plasticizer can also be used. Especially,process oil having chemical resistance is effective.

[0036] The thickness of each film obtained as described above is 0.0001to 2 mm. A thickness smaller than 0.0001 mm involves a potential problemin that a homogeneous film may not be obtained. A thickness greater than2 mm, on the other hand, makes it difficult to form the solidifyingmaterial into a film and, even if such a film is obtained, a long timeis needed for the absorption of the electrolyte. Moreover, such a greatthickness cannot provide a thin cell.

[0037] (Third Aspect of the Present Invention)

[0038] The solidifying material according to the third aspect of thepresent invention is characterized in that the solidifying materialcomprises a film or sheet of a polymer having properties the thatpolymer is insoluble in the cell electrolyte solution but the polymerabsorbs and solidifies the cell electrolyte solution, and a backingreinforcing the film or sheet; and the backing is a woven fabric, anonwoven fabric or a porous film. Preferred examples of theabove-described solidifying material can be the block copolymer in thefirst aspect of the present invention and the graft copolymer in thesecond aspect of the present invention. Other polymers can also be used.

[0039] Illustrative of such other polymers are those obtained bycrosslinking hydrophilic polymers (i.e., so-called superabsorbentpolymers). As these superabsorbent polymers, conventionally knownsuperabsorbents are all usable, and no particular limitation is imposedthereon. Illustrative are starch-based graft copolymers such as ahydrolysis product of starch-acrylonitrile graft copolymer,starch-acrylic acid graft copolymer, starch-styrenesulfonic acid graftcopolymer, starch-vinylsulfonic acid graft copolymer, andstarch-acrylamide copolymer; cellulose derivatives such ascellulose-acrylonitrile graft copolymer, cellulose-styrene-sulfonic acidgraft copolymer, and a crosslinked product of carboxymethylcellulose;hyaluronic acid, agarose, and collagen; polyvinyl alcohol derivatives,such as crosslinked polyvinyl alcohol polymer and polyvinyl alcoholsupersorbent gel/elastomer; crosslinked polyacrylic acid polymer, sodiumacrylate-vinyl alcohol copolymer, saponified product ofpolyacrylonitrile polymer, hydroxyethyl methacrylate polymer, maleicanhydride (co)polymers, vinylpyrrolidone (co)polymers, crosslinkedpolyethylene glycol-diacrylate polymer, crosslinked polypropyleneglycol-diacrylate polymer, ester-base polymers, amide-based polymers,poly[(2-oxo-1,3-dioxolan-4-yl)methyl (meth)acrylate],poly(N,N′-dimethyl-acrylamide), poly (N-vinylacetamide); and crosslinkedproducts thereof. These supersorbent polymers can absorb electrolytesolutions. Each of these superabsorbent polymers can be fixed on abacking, which will be described subsequently herein, by using adispersion in which the polymer has been dispersed with an appropriatedispersant in a non-aqueous medium.

[0040] In cadmium-nickel cells or nickel-hydrogen secondary cells,uncrosslinked copolymers each of which has been obtained using acrylicacid (or an acrylate salt), acrylamide or the like as a principalcomponent and has a weight average molecular weight of from 50,000 to1,000,000 can be used in place of the above-described (cc)polymers.

[0041] In lithium cells as typical examples of those making use ofnon-aqueous electrolyte solutions, polymers obtained by copolymerizingmonomeric esters or the like to the above-described polymers can beused. Examples of such monomeric esters can include methyl (meth)acrylate, ethyl (meth) acrylate, n-butyl (meth)acrylate, isobutyl(meth)acrylate, tert-butyl (meth)acrylate, lauroyl (meth)acrylate,stearyl (meth)acrylate, acrylonitrile, styrene, and vinyl acetate. Tostrengthen the solidifying material which has swollen as a result ofabsorption of the electrolyte solution, the above-describedpolyfunctional monomer may be copolymerized in a small proportion tocrosslink the solidifying material.

[0042] As a polymerization catalyst, conventionally known radicalpolymerization initiators are all usable, and no limitation is imposedon the polymerization catalyst. Illustrative are azobisisobutyronitrile,azobiscyanovaleric acid, benzoyl peroxide, lauroyl peroxide,cumenehydroperoxide, ammonium persulfate and alkali salts thereof, andhydrogen peroxide. It is also possible to conduct the polymerization inthe presence or absence of such a polymerization catalyst, underirradiation of ultraviolet rays, electron beams or radiation, or underheat.

[0043] When the electrolyte is an aqueous solution, the solidifyingmaterial may preferably contain ion-compatible groups. When theelectrolyte is a non-aqueous solution, it is important for thesolidifying material to contain polyethylene oxide groups which takepart in the transfer of alkali ions. The amount of the electrolyte to beabsorbed in the solidifying material can be in a range of from 5 to5,000 wt. % based on the solidifying material. An absorption smallerthan 5 wt. % cannot provide the solidified electrolyte solution withsufficient electrical conductivity, while an absorption greater than1,000 wt. % results in swollen gel (the solidifying material in aswollen form as a result of absorption of the electrolyte solution) ofconsiderably reduced strength.

[0044] Among the above-described solidifying materials, the solidifyingmaterial according to the third aspect of the present invention isgenerally used after mechanically grinding it to a particle size of 100μm or smaller, preferably 50 μm or smaller. Inclusion of particlesgreater than 100 μm makes it difficult to form a thin, film-shapedsolidifying material. On the other hand, the solidifying materialsaccording to the first and second aspects of the present invention, eachof which contains the segments A, feature good dispersibility in otherpolymers having no compatibility with the electrolyte solution, andtheir particle sizes can be easily reduced to several 100 nm to 10 μm.

[0045] The solidifying material according to the third aspect of thepresent invention is composed of the above-described solidifyingmaterial and the reinforcing backing. To improve the formability of thesolidifying material and the strength of the thus-formed product, it ispreferred to add, to the solidifying material, a polymer havingelastomeric property but no compatibility with the electrolyte solution.Such a polymer can be any one of the natural and synthetic rubbersdescribed above in connection with the first and second aspects of thepresent invention.

[0046] To reinforce the solidifying material, a woven fabric, a nonwovenfabric or a porous film can be used as a backing. The materials of thesebackings are, for example, polyethylene, polypropylene, polyamides,polyacrylonitrile, polyesters, polyvinyl chloride, and polyvinylfluoride. Polyethylene, polypropylene and polyacrylonitrile arepreferred for their excellent chemical resistance. In the case of anaqueous electrolyte solution, use of a hydrophilic backing with sulfonicgroups or the like introduced therein is preferred in order to stabilizea coating formulation containing the solidifying material. Alsopreferred is a backing obtained by hydrolyzing a woven fabric ornonwoven fabric of polyacrylonitrile fibers at surfaces thereof withconcentrated sulfuric acid or the like to introduce carboxyl groupstherein. It is sufficient to apply such treatment only to fibersurfaces.

[0047] The woven fabric, nonwoven fabric or porous film as the backingmay preferably have a thickness in a range of from 1 to 1,200 μm, morepreferably from 2 to 400 μm. A thickness smaller than 1 μm makes itdifficult to produce such a woven fabric, nonwoven fabric or porousfilm, while a thickness greater than 1,200 μm makes it difficult to forma thin, film-shaped solidifying material. The opening percentage of thenonwoven fabric Lay preferably in a range of from 95 to 10%. An openingpercentage higher than 95% bring about only small reinforcing effect forthe solidifying material, while an opening percentage lower than 10%leads to a film of extremely low electrical conductivity afterabsorption and solidification of the electrolyte. No particularlimitation is imposed on the type of weave of the woven fabric, andexamples of the weave can include plain weave, twilled weave, plaindutch weave and twilled dutch weave.

[0048] As a process for fixing the solidifying material on thereinforcing backing, (1) the reinforcing backing is dipped in a coatingformulation (a dispersion of the solidifying material), is squeezedthrough a mangle or the like, and is then dried, (2) the coatingformulation is coated onto the reinforcing backing by a gravure coater,a comma (knife) coater, a reverse coater or a blade coater, and is thendried, (3) the solidifying material is formed into a film in a manner bya known method, and the film is then bonded onto the reinforcing backing(for example, a cast film of the solidifying material is bonded underpressure through heated rolls or on a press. In some instances, thecoating formulation can be fixed on the reinforcing backing by coatingthe coating formulation onto the reinforcing backing, immersing thethus-coated reinforcing backing in a poor solvent to make the layer ofthe solidifying material porous, and then drying the reinforcing backingwith the resultant porous layer carried thereon.

[0049] No particular limitation is imposed on a process for having theelectrolyte solution absorbed in the solidifying material according tothe present invention. For example, it is possible to have theelectrolyte solution absorbed in the solidifying material in the form ofa film reinforced with the reinforcing backing. As an alternative, it isalso possible to add the electrolyte solution to a solution of thesolidifying material and, subsequent to having the resultant solutionabsorbed in the reinforcing backing in the form of a film reinforcedwith the reinforcing backing, to conduct drying to obtain thesolidifying material in the form of the film with the electrolytesolution absorbed therein. In some instances, it is also possible tohave the electrolyte solution absorbed in the solidifying material bybonding a backing on each electrode of a cell, dipping the electrode ina solution of the solidifying material with the backing bonded on theelectrode or coating the solution onto the backing on the electrode, andthen conducting drying. This process is effective for improving themutual contact between the electrode and the film, which has been formedby solidifying the electrolyte solution, at the interface therebetween.

[0050] Examples of a cell electrolyte to be absorbed in theabove-described solidifying materials according to the first to thirdaspects of the present invention can include dilute sulfuric acid,potassium chloride, zinc chloride, potassium hydroxide, and lithiumsalts such as lithium perchlorate, LiBF, LiPF₆, LiCF₃SO₃, LiN(CF₃SO₂)₂and LiC(CF₃SO₂)₂.

[0051] Illustrative of a medium in the above-described electrolytesolution are water, ethylene carbonate, propylene carbonate, dimethylcarbonate, ethyl methyl carbonate, dimethyl carbonate, γ-butyrolactone,methyl formate. methyl acetate, dimethyl sulfoxide, acetonitrile,N-methyl-pyrrolidone, tetrahydrofuran, diethylene glycol dimethyl ether,diethyl ether, 1,2-dimethoxyethane, and mixtures thereof.

[0052] The present invention will next be described more specificallybased on Examples and Referential Examples, in which designations of“part” or “parts” and “%” are each on a weight basis unless otherwisespecifically indicated.

[0053] (First Aspect of the Present Invention)

EXAMPLE 1 Production Example of a Solidifying Material A

[0054] A block copolymer (15 parts) composed of polystyrene,polybutadiene and polystyrene (polystyrene content: 30%, weight averagemolecular weight: 100,000) was dissolved in a mixed solvent formed oftoluene (45 parts), cyclohexane (75 parts) and methyl ethyl ketone (35parts), and the resulting solution was heated to 70° C. under a nitrogengas stream. Into the solution, thioglycolic acid (20 parts) andazobisisobutyronitrile (0.3 part) were added, followed by an additionreaction for 12hours. The reaction mixture was washed with a saturatedaqueous solution of Na₂SO₄ to extract off unreacted thioglycolic acidfrom the reaction mixture. A 15% solution of potassium hydroxide inmethanol was added to the thus-washed solution to convert carboxylgroups in the resultant solidifying material into potassium salts.

[0055] The solvent was then distilled off to adjust the solid content ofthe solution to 30%. As a result of an analysis of the solid matter inthe solution by infrared absorption spectroscopy, the unsaturated groupsof the polybutadiene were confirmed to be substantially eliminated. Theparticle size of particles suspended in the solution was measured by thelight scattering method (Coulter A4 particle sizer). As a result, theparticles were found to have a particle size of about 100 nm. Further,the solidifying material A taken out of the solution had a swellingindex of 3,000% in deionized water.

[0056] Test 1 (Hot Potassium Hydroxide Durability Test)

[0057] The above-described solidifying material A was placed in a 20%aqueous solution of potassium hydroxide (electrolyte solution) and wascontinuously left over at 80° C. for 3 months. The absorption of thepotassium hydroxide solution in the solidifying material A was 400%, andno changes were observed on the solidifying material A.

[0058] Test 2

[0059] The above-prepared solution of the solidifying material A, thesolid content of which was 30%, and a solution (solid concentration:20%) of a polystyrene-polybutadiene-polystyrene (SBR-TR) block copolymer(polystyrene content: 30%, weight average molecular weight: 100,000) intoluene/methyl ethyl ketone were mixed at the respective solid ratios(weight ratios) described in Table 1. The resultant liquid mixtures werecast and dried on glass plates to form films of about 100 μm inthickness, respectively.

[0060] In Table 1, liquid absorption rates of each film are showntogether with the corresponding electrical conductivity data of the filmin forms with liquids absorbed therein. The liquid absorption rates weredetermined as will be described next. Samples of the film were immersedin solutions (deionized water, and a 10% aqueous solution of potassiumchloride), respectively. From weight changes of the film samples afterthe immersion, the liquid absorption rates were calculated. On the otherhand, the electrical conductivities were determined as will be describednext. Samples of the film were immersed at 25° C. for 24 hours in the 3months in the solutions (the deionized water, and the 10% aqueoussolution of potassium chloride), respectively. The film samples weretaken out of the solutions, and were sandwiched between platinum platesof 1 cm². Across the respective film samples, voltages of 6V wereapplied, respectively. From the resulting currents, the electricalconductivities were calculated. TABLE 1 Electrical Electricalconductivity Absorption conductivity of film with Absorption rate ofSolidifying Electrical of film with aqueous rate of aqueous material A/conductivity deionized solution of deionized solution SBR-TR of dry filmwater absorbed KCl absorbed water of KCl (weight ratio) (Ω⁻¹cm⁻¹)(Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (wt. %) (wt. %)  0/100 0 0 0 0 0 25/75  1.2 × 10⁻⁷ 5.7 × 10⁻³ 5.8 × 10⁻³ 250 150 50/50 2.45 × 10⁻⁶ 1.29 × 10⁻³ 6.9 × 10⁻³450 200 75/25 6.94 × 10⁻⁵ 2.42 × 10⁻³ 4.36 × 10⁻²  700 250 100/0   7.8 ×10⁻⁴  5.1 × 10⁻² 7.7 × 10⁻² 3,000 300

[0061] It has been found from Table 1 that, when the content of thesolidifying material A is 25% or higher, films with the respectivesolutions absorbed therein show sufficient electrical conductivities.From these results, it is understood that the solidifying materialaccording to the present invention is useful as a solidifying materialfor electrolyte solutions in “CADNICA” cells (Ni—Cd cells) ornickel-hydrogen cells.

EXAMPLE 2 Production Example of a Solidifying Material B

[0062] A block copolymer (8 parts) composed ofpolystyrene-polybutadiene-polystyrene (polystyrene content: 30%, weightaverage molecular weight: 100,000) was dissolved in a mixed solventformed of a petroleum-base solvent (50 parts) and methyl ethyl ketone(80 parts), and the resulting solution was heated to 70° C. under anitrogen gas stream. Into the solution, thioglycerin (12 parts) andazobisisobutyronitrile (0.2 part) were added, followed by an additionreaction for 12 hours. After completion of the reaction, the reactionmixture was washed with a saturated aqueous solution of Na₂SO₄ toextract off unreacted thioglycerin from the reaction mixture.

[0063] Ethylene oxide was blown into the solution in the presence of analkali catalyst to have 3 moles of ethylene oxide added per hydroxylgroup. The particle size of fine particles in the solution was measuredby the light scattering method (Coulter N4 particle sizer). As a result,the particle size was found to be about 200 nm. The swelling index of asolidifying material B, which had been taken out of the solution, indeionized water was 2,000%.

[0064] Incidentally, the solidifying material B can also absorb othersolvents such as tetrahydrofuran, dimethylformamide and methyl ethylketone to about 500 to 1,000%. Therefore, the solidifying material B canalso be used as a solidifying material for lithium cell electrolytesolutions containing aprotic solvents.

[0065] (Second Aspect of the Present Invention)

EXAMPLE 3 Production Example of a Solidifying Material C

[0066] Acrylic acid (30 parts), polyethylene glycol monomethacrylate (70parts, weight average molecular weight: about 300) andmethacryloyl-containing polystyrene (30 parts, weight average molecularweight: about 6,000) were dissolved in a mixed solvent formed of methylethyl ketone (100 parts) and cyclohexane (180 parts).Azoisobutyronitrile (1.1 parts) was mixed with the solution, followed bypolymerization at 70° C. for 8 hours under a nitrogen gas stream. Aftercooling, the carboxyl groups in the resulting solidifying material Cwere neutralized with a 15% solution of caustic potash in methanol. Thesolvent was distilled off to adjust the solid content to 50%. Theparticle size of the solidifying material C in the solution was about300 nm. The absorption rate of the solidifying material C, which hadbeen taken out of the solution, in deionized water was about 2,000%based on its weight.

[0067] Test 3

[0068] The above-prepared solution of the solidifying material C and asolution (solid concentration: 20%) of apolystyrene-polybutadiene-polystyrene (SBR-TR) block copolymer(polystyrene content: 30%, weight average molecular weight: 100,000) intoluene/methyl ethyl ketone were mixed at the respective weight ratios(solid ratios) described in Table 2. The resultant liquid mixtures wereformed by casting into films of about 100 μm in thickness, respectively.Measurements of their liquid absorption rates and electricalconductivities were conducted by the same methods as in Test 1. TABLE 2Electrical Electrical conductivity Absorption conductivity of film withAbsorption rate of Solidifying Electrical of film with aqueous rate ofaqueous material C/ conductivity deionized solution of deionizedsolution SBR-TR of dry film water absorbed KCl absorbed water of KCl(weight ratio) (Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (Ω⁻¹cm⁻¹) (wt. %) (wt. %)  0/100 0 00 0 0 25/75  1.2 × 10⁻¹¹ 1.1 × 10⁻³ 2.8 × 10⁻³ 250 160 50/50 1.0 × 10⁻⁶1.1 × 10⁻² 1.4 × 10⁻² 350 200 75/25 2.9 × 10⁻⁶ 2.2 × 10⁻² 8.4 × 10⁻² 510220

[0069] It has been found from Table 2 that films, each of which containsthe solidifying material of the present invention at 25% or more andcontains an electrolyte solution absorbed therein, show sufficientelectrical conductivities. From these results, it is understood that thesolidifying material according to the present invention is useful as asolidifying material for electrolyte solutions in “CADNICA” cells (Ni—Cdcells) or nickel-hydrogen cells. Further, the solidifying materialaccording to the present invention can also absorb solvents other thanwater, such as tetrahydrofuran, dimethylforamide and methyl ethylketone, at rates of from about 300 to 800%. Therefore, the solidifyingmaterial according to the present invention can also be used as asolidifying material for lithium cell electrolyte solutions containingaprotic solvents.

[0070] (Third Aspect of the Present Invention)

EXAMPLE 4 Production Example of a Solidifying Material D

[0071] Following the process disclosed in JP 55-56615 A, potassiumthioglycolate was added to 95 mole % of the double bonds ofpolybutadiene in a block copolymer composed ofpolystyrene-polybutadiene-polystyrene (polystyrene content: 40%, weightaverage molecular weight: 150,000) to produce a solidifying material D.

[0072] A mixed solution of toluene/cyclohexane/MEK (35/35/30, weightratio) and the solidifying material D were mixed to adjust the solidcontent to 25%. The average dispersed particle size of the solidifyingmaterial D in the solution was measured by the light scattering method(Coulter A4 particle sizer) (this will apply equally hereinafter). As aresult, the average dispersed particle size was found to be about 100nm. The swelling index of the solidifying material D in deionized waterwas 100-fold.

EXAMPLE 5 Production Example of a Solidifying Material E

[0073] In a similar manner as described above, thioglycol was added to90 mole % of the double bonds of polybutadiene in a block copolymerpolystyrene-polybutadiene-polystyrene (polystyrene content: 30%, weightaverage molecular weight: 100,000), and ethylene oxide (7 moles onaverage) was added to the hydroxyl groups of the thioglycol to produce asolidifying material E. The solidifying material E was mixed with amixed solvent of toluene/cyclohexanone/MEK (35/35/30, weight ratio) toadjust the solid content to 20%. The average dispersed particle size ofthe solidifying material E in the solution was about 100 nm. Theswelling index of the solidifying material E in deionized water was10-fold.

EXAMPLE 6 Production Example of a Solidifying Material F

[0074] A solidifying material F composed of potassium acrylate,polyethylene glycol monomethacrylate (molecular weight: about 300) andmethacryloyl-containing polystyrene (molecular weight: about 6,000)[weight ratio: 70/30/20%] was mixed with a mixed solvent of methyl ethylketone/cyclohexane (60/40, weight ratio) to adjust the solid content to50%. The average dispersed particle size of the solidifying material Fin the solution was about 300 nm. The swelling index of the solidifyingmaterial F in deionized water was 30-fold.

EXAMPLE 7 Production Example of a Solidifying Material G

[0075] A crosslinked polymer composed of potassiumacrylate/N,N′-methylenebisacrylamide (99.5/0.5%) was produced as asolidifying material G by radical polymerization. The content ofwater-soluble components in the solidifying material G was 20%. Theswelling index of the solidifying material G in deionized water was200-fold.

EXAMPLE 8 Production Example of a Solidifying Material H

[0076] A commercial, crosslinked isobutylene/potassium maleate copolymer(isobutylene/potassium maleate=1/1, molar ratio) was provided as asolidifying material H. The swelling index of the solidifying material Hin deionized water was 320-fold.

EXAMPLE 9 Production Example of a Solidifying Material I

[0077] Crosslinked poly(N-vinylacetamide) obtained by radicalpolymerization was provided as a solidifying material I. The swellingindex of the solidifying material I in deionized water was 25-fold.

EXAMPLE 10 Production Example of a Solidifying Material J

[0078] Poly(sodium acrylate) produced by reverse-phase polymerizationand having an average particle size of 200 μm was provided as asolidifying material J. The swelling index of the solidifying material Jin deionized water was 1,000-fold.

EXAMPLE 11 Production Example of a Solidifying Material K

[0079] An acrylic acid (89.1%)/styrene (10%)/divinylbenzene (0.9%,purity: 55%) copolymer, which had been obtained by bulk polymerizationin the presence of azobutyronitrile as a polymerization initiator, wasneutralized with potassium hydroxide, dried, and then ground. Fineparticles of from 1 to 5 μm in particle size were provided as asolidifying material K. The swelling index of the solidifying material Kin deionized water was 130-fold.

[0080] The following reinforcing backings were provided:

[0081] (1) Woven fabric obtained by sulfonating the surfaces of apolypropylene fabric (thickness: 0.122 mm, basis weight: 33 g/m², threadthickness: 0.080 mm, opening diameter: 0.098 mm).

[0082] (2) Nonwoven fabric (A) obtained by treating a nonwovenpolyacrylonitrile fabric (thickness: 0.081 mm, basis weight: 45 g/m²)with sulfuric acid to hydrolyze fibers at the surfaces thereof andforming potassium salts.

[0083] (3) Nonwoven fabric (B) obtained by sulfonating a nonwoven fabric(polypropylene fibers, thickness: 0.1 mm, basis weight: 33 g/m², airresistance: 3 sec/L) at surfaces thereof.

EXAMPLE 12 Production Example of a Solidifying Film 1

[0084] The solidifying material D, a polystyrene-polybutadiene blockcopolymer (styrene content: 30%, weight average molecular weight:100,000; these will apply equally hereinafter) and an aromatic processoil were mixed at a weight ratio of 64/21/15 with toluene to adjust thesolid content to 20%. A coating formulation of the solidifying materialwas obtained accordingly. The coating formulation was applied onto bothsides of the woven fabric (1), and then dried at 80° C. for 24 hours toobtain a solidifying film 1 of 0.11 mm in thickness (coat weight: 100g/m² weight basis; this will apply equally hereinafter).

EXAMPLE 13 Production Example of a Solidifying Film 2

[0085] The solidifying material F and the polystyrene-polybutadieneblock copolymer were mixed at a weight ratio of 75/25 with toluene toadjust the solid content to 20%. A coating formulation was obtainedaccordingly. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 2 of 0.15 mm in thickness (coat weight: 100 g/m²).

EXAMPLE 14 Production Example of a Solidifying Film 3

[0086] The solidifying material G and the polystyrene-polybutadieneblock copolymer were mixed at a weight ratio of 70/30 with toluene toadjust the solid content to 20%. A coating formulation was obtainedaccordingly. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 3 of 0.2 mm in thickness (coat weight: 100 g/m²).

EXAMPLE 15 Production Example of a Solidifying Film 4

[0087] The solidifying material G and the polystyrene-polybutadieneblock copolymer were dispersed at a weight ratio of 70/30 in toluene bya “Dynomil” (high-speed bead mill) to adjust the solid content to 20%. Acoating formulation was obtained accordingly. The average dispersedparticle size of the solidifying material in the coating formulation wasabout 30 μm. The coating formulation was applied onto both sides of thewoven fabric (1), and then dried at 80° C. for 24 hours to obtain asolidifying film 4 of 0.2 mm in thickness (coat weight: 100 g/m²).

EXAMPLE 16 Production Example of a Solidifying Film 5

[0088] The solidifying material H and the polystyrene-polybutadieneblock copolymer were dispersed at a weight ratio of 70/30 intetrahydrofuran by a “Dynomill” (high-speed bead mill) to adjust thesolid content to 30%. A coating formulation was obtained accordingly.The average dispersed particle size of the solidifying material in thecoating formulation was about 25 μm. The coating formulation was appliedonto both sides of the woven fabric (1), and then dried at 80° C. for 24hours to obtain a solidifying film 5of 0.12 mm in thickness (coatweight: 100 g/m²).

EXAMPLE 17 Production Example of a Solidifying Film 6

[0089] The solidifying material I and the polystyrene-polybutadieneblock copolymer were dispersed at a weight ratio of 90/10 intetrahydrofuran by a “Dynomill” (high-speed bead mill) to adjust thesolid content to 30%. A coating formulation was obtained accordingly.The average dispersed particle size of the solidifying material in thecoating formulation was about 35 μm. The coating formulation was appliedonto both sides of the woven fabric (1), and then dried at 80° C. for 24hours to obtain a solidifying film 6 of 0.12 mm in thickness (coatweight: 100 g/m²)

EXAMPLE 18 Production Example of a Solidifying Film 7

[0090] The solidifying material D, the polystyrene-polybutadiene blockcopolymer and an aromatic process oil were mixed at a weight ratio of64/21/15 with toluene to adjust the solid content to 20%. A coatingformulation was obtained accordingly. The coating formulation wasapplied onto both sides of the woven fabric (A), and then dried at 80°C. for 24 hours to obtain a solidifying film 7 of 0.9 mm in thickness(coat weight: 40 g/m²).

EXAMPLE 19 Production Example of a Solidifying Film 8

[0091] The solidifying material D, the polystyrene-polybutadiene blockcopolymer and an aromatic process oil were mixed at a weight ratio of64/21/15 with toluene to adjust the solid content to 20%. A coatingformulation was obtained accordingly. The coating formulation wasapplied onto both sides of the woven fabric (B), and then dried at 80°C. for 24 hours to obtain a solidifying film 8 of 0.12 mm in thickness(coat weight: 45 g/m²)

EXAMPLE 20 Production Example of a Solidifying Film 9

[0092] A solidifying film 9 (coat weight: 10 g/m²) was obtained in ansimilar manner as in Example 16 except that the nonwoven fabric (B) andthe solidifying material K were used instead of the woven fabric (1) andthe solidifying material H, respectively.

REFERENTIAL EXAMPLE 1 Production Example of a Solidifying Film 10

[0093] A cast film (solidifying film) 10 of 100 μm in thickness withoutthe woven fabric in Example 12 was produced.

REFERENTIAL EXAMPLE 2 Production Example of a Solidifying Film 11REFERENTIAL EXAMPLE 2 Production Example of a Solidifying Film 11

[0094] The solidifying material J and the polystyrene-polybutadieneblock copolymer were dispersed at a weight ratio of 70/30 in toluene bya “Dynomill” (high-speed bead mill) to adjust the solid content to 30%.A coating formulation was obtained accordingly. The average dispersedparticle size of the solidifying material in the coating formulation wasabout 200 μm. The coating formulation was applied onto both sides of thewoven fabric (B), and then dried at 80° C. for 24 hours to obtain asolidifying film 11 (coat weight: 100 g/m², thickness: not accuratelymeasurable as the thickness was not even).

[0095] Test 4

[0096] The individual solidifying films of the above-described Examplesand Referential Examples were ranked in the following properties. Theresults are shown in Table 3.

[0097] (1) Strength of Solidifying Film

[0098] Using each film of 15 mm in width, its tensile strength wasmeasured at a tensile speed of 100 mm/min by a strength measuringmachine (“Strograph EL”, trade name; manufactured by Toyo SeikiSeisaku-sho, Ltd.) under an environment of 20° C. and 60% RH. Eachsample was measured 10 times, and an average of the measurement resultswas recorded as measurement data.

[0099] (2) Electrical Conductivity

[0100] Samples of each film were immersed at 20° C. for 24 hours in a10% aqueous solution of potassium chloride and deionized water,respectively, and were then taken out. The samples were each heldbetween two platinum plates of 1 cm². From currents produced uponapplication of voltages of 6V across the samples, respectively, theelectrical conductivities of the samples were calculated.

[0101] (3) Liquid Absorption Rate (%)

[0102] Each film was immersed at room temperature for 24 hours in a 10%aqueous solution of potassium chloride, and was then taken out. Afterthe surfaces of the film were wiped, the weight of the film wasdetermined. The liquid absorption rate (%) of the sample was calculatedin accordance with the following formula.

[0103] <When no Backing Was Included>

Liquid absorption rate (%)=[(W ₁ −W ₀)/W ₀]×100

[0104] W₁: Weight of the film after liquid absorption (g/m²)

[0105] W₀: Weight of the film before liquid absorption (g/m²)

[0106] <When a Backing Was Included>

Liquid absorption rate (%)=[(W ₁ −W _(s) −W ₀)/(W ₀−W_(s))]×100

[0107] W₁: Weight of the film after liquid absorption (g/m²)

[0108] W₀: Weight of the film before liquid absorption (g/m²)

[0109] W_(s): Weight of the backing (g/m²)

[0110] (4) Surface Condition

[0111] Each coating formulation was applied onto a woven fabric ornonwoven fabric. The coated surface was visually observed. The surfacecondition was ranked in accordance with the following standards.

[0112] A: Extremely smooth and uniform.

[0113] B: Smooth and good uniformity.

[0114] C: Rugged, and coating was difficult. TABLE 3 Film Electricalconductivity (Ω⁻¹m⁻¹) Liquid absorption rate (%) Surface strength KClsolution Water KCl solution Water condition Ex. 12 78 40 × 10⁻⁴ 10 ×10⁻⁴ 230 4,000 A Ex. 13 80.5 33 × 10⁻⁴  7 × 10⁻⁴ 200 800 A Ex. 14 101 80× 10⁻⁴ 45 × 10⁻⁴ 400 10,000 B Ex. 15 92 72 × 10⁻⁴ 35 × 10⁻⁴ 350 20,000 BEx. 16 70 35 × 10⁻⁴ 20 × 10⁻⁴ 270 10,000 B Ex. 17 15 48 × 10⁻⁴ 15 × 10⁻⁴300 1,500 A Ex. 18 25 20 × 10⁻⁴ 10 × 10⁻⁴ 150 1,000 A Ex. 19 120 35 ×10⁻⁴  7 × 10⁻⁴ 200 3,000 A Ex. 20 80 75 × 10⁻⁴ 50 × 10⁻⁴ 1,500 7,500 ARef. Ex. 1 2 57 × 10⁻⁴ 50 × 10⁻⁴ 200 3,500 A Ref. Ex. 2 100 0.1 × 10⁻⁴ Measurement 350 10,000 C (substantial was scattering of impossiblemeasurement data)

EXAMPLE 21 Production Example of Solidifying Film 12

[0115] The solidifying material E, the polystyrene-polybutadiene blockcopolymer, lithium perchlorate, ethylene carbonate and propylenecarbonate were mixed at a weight ratio of 1/0.5/1/10/10 withtetrahydrofuran to adjust the solid content to 20%. A coatingformulation was obtained accordingly. The coating formulation wasapplied onto both sides of the woven fabric (A), and then dried at 60°C. for 48 hours to obtain a solidifying film 12 of 0.12 mm in thickness.The film 12 had an ion conductivity of 2.0×10⁻³ S/cm, and was by nomeans usable in a lithium cell.

1. A solidifying material for a cell electrolyte solution, characterizedin that said solidifying material is a block copolymer comprising, assegments A, a polymer non-compatible with said cell electrolyte solutionand, as segments B, a polymer compatible with said cell electrolytesolution, and absorbs and solidifies said cell electrolyte solution; asmallest unit of said block copolymer is A-B-A; and to each of saidsegments B, at least one group selected from the group consisting of acarboxyl group, an ester group, a hydroxyl group, a sulfonic group, anamino group, a cyclic carbonate group and a polyoxyalkylene group isbonded via a —S— bond or a —C— bond.
 2. A solidifying material accordingto claim 1, wherein each of said segments A is a polymer selected fromthe group consisting of polystyrene, polyethylene and polypropylene andhaving a weight average molecular weight of from 10,000 to 500, 000 anda content of said segments A in said block copolymer is 0.5 to 70 wt. %;and each of said segments B is a polymer selected from the groupconsisting of polybutadiene, polychloroprene and polyisoprene and havinga weight average molecular weight of from 10,000 to 300,000.
 3. Asolidifying material according to claim 1, further comprising notgreater than 85 wt. %, based on said block copolymer, of an elastomernon-compatible with said cell electrolyte solution.
 4. A solidifyingmaterial according to claim 1, which is in a form of a film or sheet offrom 0.0001 to 2 mm in thickness.
 5. A solidifying material for a cellelectrolyte solution, characterized in that said solidifying material isa graft copolymer comprising, as segments A, a polymer non-compatiblewith said cell electrolyte solution and, as segments B, a polymercompatible with said cell electrolyte solution, and absorbs andsolidifies said cell electrolyte solution; and to each of said segmentsB, at least one group selected from the group consisting of a carboxylgroup, an ester group, a hydroxyl group, a sulfonic group, an aminogroup, a cyclic carbonate group and a polyoxyalkylene group is bonded.6. A solidifying material according to claim 5, wherein each of saidsegments A is a polymer selected from the group consisting ofpolystyrene, polyethylene, polypropylene, polyacrylonitrile andpoly(meth) acrylate ester having a weight average molecular weight offrom 3,000 to 20,000, and a content of said segments A in said graftcopolymer is 0.5 to 70 wt. %.
 7. A solidifying material according toclaim 5, further comprising not greater than 85 wt. %, based on saidgraft copolymer, of an elastomer non-compatible with said cellelectrolyte solution.
 8. A solidifying material according to claim 5,which is in a form of a film or sheet of from 0.0005 to 2 mm inthickness.
 9. A cell comprising, as a constituent element, a solidifyingmaterial according to any one of claims 1-8.
 10. A solidifying materialfor a cell electrolyte solution, characterized in that said solidifyingmaterial comprises a film or sheet of a polymer having properties thatsaid polymer is insoluble in said cell electrolyte solution but saidpolymer absorbs and solidifies said cell electrolyte solution, and abacking reinforcing said film or sheet; and said backing is a wovenfabric, a nonwoven fabric or a porous film.
 11. A solidifying materialaccording to claim 10, wherein said polymer is a block or graftcopolymer as defined in any one of claims 1-8.
 12. A solidifyingmaterial according to claim 10, wherein said polymer is a polymer whichcomprises, as a principal component, polyacrylic acid,poly(N-vinylacetamide), poly[(2-oxo-1,3-dioxoran-4-yl)methyl(meth)acrylate] or polyacrylamide.
 13. A solidifying material accordingto claim 10, which is in a form of particles having an average particlessize not greater than 100 μm.
 14. A solidifying material according toclaim 10, wherein said backing is made of polyethylene or polypropylene.15. A solidifying material according to claim 10, wherein said backingis a film or sheet of from 1 to 1,200 μm in thickness and of from 95 to100% in porosity.
 16. A solidifying material according to claim 10,further comprising not greater than 85 wt. %, based on said polymer, ofan elastomer non-compatible with said electrolyte solution.
 17. A cellcomprising, as a constituent element, a solidifying material accordingto any one of claims 10-16.